In order to handle a large number of interactions, enterprise software applications can use application servers, such as J2EE application servers like the WebLogic Server™ available from BEA Systems, Inc., of San Jose, Calif. These application servers can be used in clusters that can interact with one another.
Some of the services of the application servers, called singleton services should be run on only one application server of a cluster. These singleton services can include JMS servers, transaction recovery services or any other software that should be only run in a single instance.